The present invention generally relates to magnetic recording mediums such as magnetic tapes, and in particular to a magnetic recording medium for realizing satisfactory magnetic recording and reproduction in not only a standard mode but also a high picture quality mode which has a carrier frequency higher than that in the standard mode.
Presently, performances of a magnetic tape and a magnetic head are considerably improved, and correspondingly there is desired a magnetic recording and reproducing apparatus of a high picture quality with resolution higher than that of video tape recorders which are widely used. For this reason, use of a high performance magnetic tape such as a metal tape is considered in place of standard magnetic tapes for use in the video tape recorders for home use. Such a high performance magnetic tape has a residual magnetic flux density (Br) and a coercive force (Hc) higher than those of the standard magnetic tapes. An information signal is recorded on the high performance magnetic tape by use of a carrier frequency (5 MHz-7 MHz, for example) which is considerably higher than that of the standard carrier frequency (3.4 MHz-4.4 MHz, for example).
In the present specification, a recording and reproducing mode presently which is widely employed in the vido tape recorders for home use is referred to as a standard mode, whereas a recording and reproducing mode in which the carrier frequency is made higher than that of that standard mode so as to realize a high picture quality is referred to as a high quality mode. As well known, there is no interchangeability between the standard mode and the high picture quality mode. However, it is possible to carry out recording and reproduction selectively in the standard and high picture quality modes in a video tape recorder. Such a video tape recorder is designed so that there is provided two kinds of signal processing circuits corresponding to the standard and high picture quality modes and a switching means for selecting either one of the signal processing circuits.
Now let us consider a magnetic tape which is accommodated in the video tape recorder which can record and reproduce the information signal thereon and therefrom in both the standard and high picture quality modes. It is well known that there are many kinds of magnetic tapes having distinct specifications currently available in the market. In general, these magnetic tapes can be classified into two kinds of magnetic tapes, one of which is a high picture quality magnetic tape such as a so-called metal tape and the like, and the other is a standard magnetic tape using iron oxide magnetic material as a magnetic material coated on a base film.
The video tape recorder having both the standard and high picture quality modes is now considered in which recording and reproduction are carried out in the case where a high picture quality magnetic tape is loaded therein. There are some problems in the optimum recording current or recording characteristics at short wave length and therefore reproduction of the video signal is not so good. And, when the video tape recorder is in the standard mode, a long wavelength recording characteristic relating to the recording and reproduction of an audio signal is noticeably degraded. For this reason, it is impossible to use the high picture quality magnetic tape in the standard mode.
In addition, it is considered that the recording and reproduction are carried out in a state where a standard magnetic tape is accommodated in the video tape recorder having both the standard and high picture quality modes. With the video tape recorder set in the high picture quality mode, the standard magnetic tape is not suited for the high picture quality mode from the point of view of its performance characteristics. Even when the recording based on the high picture quality mode is performed for the standard magnetic tape, a over modulation (the carrier signal which fails to be reproduced at the edge in reproduced picture brings about a reverse phenomenon between white and black) and/or an edge noise occurs (the noise observed near the bar edge in reproduced picture) on a reproduced picture. For this reason, it is impossible to use the standard tape in the high picture quality mode.
As will be anticipated from the above description, when trying to use the marketed magnetic tapes for the video tape recorder in which the standard and high picture quality modes are selectively switchable, it is necessary to select the magnetic tapes to suit the respective modes to be used. In other words, a magnetic tape which can be commonly used in each of the modes does not exist.